1. Field of the Invention
The present invention relates to image display apparatus so called head-mounted displays and the like.
2. Related Background Art
For the image display apparatus such as the head-mounted displays and the like, various proposals have been made heretofore on optical systems for compactification of the entire apparatus. For example, Japanese Patent Application Laid-Open No. 7-333551 (corresponding to EP687932A3) describes a proposal on an apparatus using an optical element of prism shape composed of first, second, and third rotationally asymmetric surfaces and constructed to display an enlarged image through the three surfaces of the optical element from an image on a display surface of an image display element.
By use of the optical element of such prism shape, it becomes feasible to correct distortion of image, curvature of field, and astigmatism well in very compact and simple structure and satisfy the telecentric condition to the display surface.
At the time of this proposal of the above application, it was common practice to use a transmissive liquid crystal display as the image display element. However, since pixel apertures are small in the transmissive liquid crystal displays, the transmissive liquid crystal displays have the drawback that it is difficult to achieve both high pixel density and compactification. In recent years, in addition to motion pictures of videos, TVs, and so on, output devices of high-definition images such as personal computers, DVDs, and so on have been increasing and there are desires for display of much higher definition images.
Under such circumstances, high-definition images can be obtained by use of reflective liquid crystal displays having larger pixel apertures while achieving the compactification. An example of the display devices using the reflective liquid crystal displays proposed so far is one proposed in Japanese Patent Application Laid-Open No. 11-125791. This application discloses the display device, as illustrated in FIG. 1 of the present application, in which rays 113 from a light source 112 are guided directly onto a reflective liquid crystal display 108 without passing through an optical element and in which an image of the liquid crystal display 108 is displayed as an enlarged virtual image by an optical element 110 of prism shape to be guided to the eye 101 of an observer.
In this display device, however, since the rays 113 from the light source 112 illuminating the reflective liquid crystal display 108 are guided directly onto the liquid crystal display 108, an angle a is large between the illumination light 113 and the optical axis of the liquid crystal display 108. For this reason, the entire display device becomes large in scale and, in addition, since the liquid crystal display is largely inclined relative to the optical element 110, distances between the optical element 110 and the liquid crystal display 108 are largely different depending upon locations, which poses a problem of degradation of optical performance.
Another display device disclosed in the Japanese Patent Application Laid-Open No. 11-125791 is constructed, as illustrated in FIG. 2, in such structure that the light source 112 is disposed on the opposite side to the reflective liquid crystal display 108 with respect to the optical element 110 of the prism shape, the illumination light 113 from the light source 112 illuminates the liquid crystal display 108 through the optical element 110, and the light illuminating the liquid crystal display 108 is reflected by this liquid crystal display 108 and travels again through the optical element 110 into the observer""s eye 101.
With the illumination system of the display device of this type, however, the illumination light is reflected on each of the surfaces of the optical element 110, so that light not illuminating the liquid crystal display 108 also enters the eye 101, thus posing a problem of occurrence of unwanted flare.
An object of the present invention is to provide image display apparatus using the reflective display element ready for high-definition images of output from personal computers and the like and image display apparatus in extremely simple and compact structure without occurrence of unnecessary light, which can be the cause of flare, ghost, and so on.
In order to accomplish the above object, an image display apparatus of one embodiment of the present invention comprises a light source for supplying illumination light, a reflective display element for reflecting and modulating the illumination light into image light, a first optical system for guiding the illumination light to the reflective display element, and a second optical system for guiding the image light to an observer; particularly, the first optical system has an optical element comprising a first surface into which the illumination light is incident, a second surface for totally reflecting the light incident into the first surface, and a third surface from which the light totally reflected by the second surface emerges toward the reflective display element, the first optical system is arranged so that the image light is again incident through the third surface into the optical element and emerges from the second surface toward the second optical system, and the optical element has a function of preventing unnecessary light from being guided to the observer, by making a side surface of the optical element as a diffusing surface, or by providing a side surface of the optical element with a light absorbing film or with an antireflection coating.
An optical system of another embodiment of the present invention comprises a first optical system for guiding illumination light to a reflective display element, and a second optical system for guiding image light reflected by the reflective display element, to an observer; particularly, the first optical system has an optical element comprising a first surface into which the illumination light is incident, a second surface for totally reflecting the light incident into the first surface, and a third surface from which the light totally reflected by the second surface emerges toward the reflective display element, the first optical system is arranged so that the image light is again incident through the third surface into the optical element and emerges from the second surface toward the second optical system, and the optical element has a function of preventing unnecessary light from being guided to the observer, by making a side surface of the optical element as a diffusing surface, or by providing a side surface of the optical element with a light absorbing film or with an antireflection coating.